The present invention relates to a method for using a ventricular assist device, and more specifically is directed to a device in which the expandable member is placed directly within the left ventricle of the heart to facilitate complete ejection of the blood during systole.
In certain pathological conditions the heart, and principally the left ventricle, cannot contract fully during systole, so there is incomplete emptying of the heart. The amount of blood left in the ventricle at the end of systole is the "dead volume or space" and represents unused pumping capacity.
Damage to the left ventricular muscle arises from a variety of causes, whether chemical, physical, bacterial and viral, and leads to decrease of contractility and therefore a decrease of ejection fraction. Congestive heart failure results which may be correctable to varying degrees by pharmacological or mechanical intervention.
In intractable left ventricle failure, when it is not possible to increase the stroke volume, the "dead volume or space" is left at the end of the systole.
The prior art devices appear generally to be in the nature of U.S. Pat. No. 3,266,487 which consists of devices which are placed within the aorta. None of the devices are placed directly within the left ventricle where they can operate more efficiently. U.S. Pat. No. 3,592,183 is a ventricular assist device having an aortic balloon with a somewhat similar shape to that of the present invention, but it does not perform the same functions and it is not positioned within the left ventricle.
It is therefore an object of the present invention to provide a method for using a ventricular assist device which is designed to restore normal stroke volume.
Still yet another object of the present invention is to provide a method for using a device which restores normal stroke volume by obliterating the dead volume or space in a damaged left ventricle.
Still yet another object of the present invention is to provide a method for using a device which is inserted directly into the left ventricle and operates with greater efficiency than prior art devices.
Yet a further object of the present invention is to provide a method for using a device which may be implanted within the body of the user and is not tethered to any external operating elements.
Still yet a further object of the present invention is to provide a method for using a device which only requires connection to an external electrical source.
Still yet another object of the present invention is to provide a method for using a device which will be easy to insert and yet be capable of operating at high efficiency.
Still yet a further object of the invention is to provide a method for using a device which will be simple and economical to manufacture and yet be durable to a high degree during the time of use required by the patient.
BRIEF DESCRIPTION OF THE INVENTION
The invention is a method for using a ventricular assist device having a catheter with a proximal end and a distal end, a pump secured to the proximal end of the catheter, and an inflatable balloon secured to the distal end of the catheter. The balloon is inserted into the left ventricle of a patient's heart. The balloon is inflated during left ventricular systole, and then the balloon is deflated. The inflating and deflating steps are repeated. Preferably, the inflating step starts at approximately the beginning of left ventricular systole and stops at approximately the end of left ventricular systole. The balloon may be inserted into the heart through the mitral valve, through the aortic valve, or through the apex of the left ventricle. The pump is advantageously implanted within the patient's body, e.g., within an envelope of skeletal muscle.
The ventricular assist device may include a shaped radioopaque balloon connected to the tip of an intra-arterial catheter with a single lumen. The proximal end of the catheter is connected to a gas pump that is capable of inflating and deflating the balloon in a range of 50 to 120 cycles per minute. The gas used is either carbon dioxide or helium. The pump mechanism is triggered by an electronic relay connected to an electrocardiograph, so that inflation and deflation are governed by specific time sequences in the EKG corresponding to electrical systole and diastole.
The balloon is selected to properly fit within the left ventricular chamber, and is made to inflate just as mechanical systole begins. The cessation of inflation corresponds to the end of mechanical systole. Active contraction of the balloon begins at the onset of mechanical diastole. The negative pressure thus generated increases the pressure gradient between the left atrium and left ventricle, thus augmenting diastolic filling. This sequence of events enables the balloon to expand meeting the incoming (contracting) walls of the ventricle, thus obliterating the dead space and augmenting stroke volume. Since the Mitral valve is closed, and the Aortic valve is open, all the blood ejected flows distally into the aorta in a physiologic manner.
While it is possible to operate the ventricular assist device by means of external manipulation as is done in prior art devices, it is preferred to have the device wholly implanted within the body of the user, requiring no external equipment for proper operation. This is possible by creating a muscle pump, for example, by using skeletal muscle with timed means to internally stimulate the muscle causing appropriate inflation and deflation of the balloon. Another modified embodiment uses a solenoid pump with contacts lying just on the outer surface of the skin, designed to be connected to an external power source. Thus, the unit can be either self-contained and has a "no tether" feature or a "no tubetether" feature.